Vibrations Of Molecules Research Articles

Infrared–vacuum ultraviolet spectroscopy of the CH stretching vibrations of jet‐cooled aromatic azine molecules and the anharmonic analysis

AbstractVibrational spectra of the CH stretching vibration of diazine molecules, pyrimidine and pyrazine, were measured by infrared (IR)–vacuum ultraviolet (VUV) spectroscopy under the jet‐cooled gas‐phase condition. The observed IR spectra were analyzed by three anharmonic algorithms to account for the Fermi‐resonance (F‐R). The anharmonic analysis of the F‐R pattern was performed with second‐order vibrational perturbation theory (VPT2) with quartic potentials (QPs) at the DFT level of B2PLYP/6–311++G(d,p), followed by vibrational configuration interaction (VCI) method with the same QP. The VPT2 + QP method reasonably reproduced most of the bands in the observed spectra for all the species, especially for pyrimidine, a decent agreement is obtained with respect to the band positions and relative intensities. The analyses of the spectra show that all the observed spectra can be well interpreted by the F‐R between the CH stretching fundamentals and the first overtone and 1 + 1 combination bands involving the in‐plane CH bending vibrations and the contribution of the higher‐order anharmonic coupling to the observed spectra seems to lead to red‐shift of the F‐R patterns. Discrete variable representation based methods with potential energy surfaces at CCSD/aug‐cc‐pVDZ theory with 10 degrees of freedom were also carried out to assess the quality of QP at DFT level.

Classification of oil palm fresh fruit maturity based on carotene content from Raman spectra

The oil yield, measured in oil extraction rate per hectare in the palm oil industry, is directly affected by the ripening levels of the oil palm fresh fruit bunches at the point of harvesting. A rapid, non-invasive and reliable method in assessing the maturity level of oil palm harvests will enable harvesting at an optimum time to increase oil yield. This study shows the potential of using Raman spectroscopy to assess the ripeness level of oil palm fruitlets. By characterizing the carotene components as useful ripeness features, an automated ripeness classification model has been created using machine learning. A total of 46 oil palm fruit spectra consisting of 3 ripeness categories; under ripe, ripe, and over ripe, were analyzed in this work. The extracted features were tested with 19 classification techniques to classify the oil palm fruits into the three ripeness categories. The Raman peak averaging at 1515 cm−1 is shown to be a significant molecular fingerprint for carotene levels, which can serve as a ripeness indicator in oil palm fruits. Further signal analysis on the Raman peak reveals 4 significant sub bands found to be lycopene (ν1a), β-carotene (ν1b), lutein (ν1c) and neoxanthin (ν1d) which originate from the C=C stretching vibration of carotenoid molecules found in the peel of the oil palm fruit. The fine KNN classifier is found to provide the highest overall accuracy of 100%. The classifier employs 6 features: peak intensities of bands ν1a to ν1d and peak positions of bands ν1c and ν1d as predictors. In conclusion, the Raman spectroscopy method has the potential to provide an accurate and effective way in determining the ripeness of oil palm fresh fruits.

Study on the characteristic spectral bands of water molecule and hydrogen bond of methane hydrate

In this study, in situ observation on the formation of methane hydrate with a laser confocal Raman imaging microscope is conducted, to reveal the interaction between the guest molecule and the lattice water molecule. The evolutions of the broad band of the stretching vibration of water molecules and intermolecular hydrogen bonds in the Raman spectrum are observed in the course of methane hydrate formation, revealing that quantitative analysis of Raman spectrum can be considered as a criterion of the disorder–order character of the water–hydrate phase transition. Moreover, based on the recognition that the characteristic peak of the hydrogen bond will change abruptly before and after the phase transition, a promising technique is proposed for field hydrate exploration and laboratory identification of hydrate growth.

Machine Learning Approach for Describing Water OH Stretch Vibrations.

A machine learning approach employing neural networks is developed to calculate the vibrational frequency shifts and transition dipole moments of the symmetric and antisymmetric OH stretch vibrations of a water molecule surrounded by water molecules. We employed the atom-centered symmetry functions (ACSFs), polynomial functions, and Gaussian-type orbital-based density vectors as descriptor functions and compared their performances in predicting vibrational frequency shifts using the trained neural networks. The ACSFs perform best in modeling the frequency shifts of the OH stretch vibration of water among the types of descriptor functions considered in this paper. However, the differences in performance among these three descriptors are not significant. We also tried a feature selection method called CUR matrix decomposition to assess the importance and leverage of the individual functions in the set of selected descriptor functions. We found that a significant number of those functions included in the set of descriptor functions give redundant information in describing the configuration of the water system. We here show that the predicted vibrational frequency shifts by trained neural networks successfully describe the solvent-solute interaction-induced fluctuations of OH stretch frequencies.

In-situ detection of sulfur in the atmosphere via laser-induced breakdown spectroscopy and single particle aerosol mass spectrometry technology

The combustion of sulfur-containing minerals is one of the primary causes of various atmospheric and water pollution issues, including sulfuric acid rain. Considering that sulfur is particularly susceptible to oxidation in the air, the direct detection of sulfur via laser-induced breakdown spectroscopy (LIBS) has presented a major challenge. In this work, CS2 was used as a sample evaporated and atomized into the air. A new experimental device that combines the LIBS system with the single particle aerosol mass spectrometry (SPAMS) system was adopted for the direct detection of sulfur in the atmosphere. Under the optimal experimental conditions, the characteristic spectral lines of sulfur were observed and recorded in the LIBS spectra. Additionally, in the LIBS spectrum, CN molecular bands were observed, and the vibration and rotation temperature of the CN molecules in the experiment were obtained through software simulation. While the SPAMS system generates the real-time composition of a single CS2 aerosol particle, the isotope information of sulfur can also be distinguished simultaneously. Sulfur isotopes are widely used as tracers in chemistry, agricultural science, and environmental science research. Finally, the LIBS and SPAMS experiment systems can perform the direct in-situ detection of sulfur in the air and provide its isotope information.

Encapsulation of a Water Molecule inside C60 Fullerene: The Impact of Confinement on Quantum Features.

We introduce an efficient quantum fully coupled computational scheme within the multiconfiguration time-dependent Hartree (MCTDH) approach to handle the otherwise extremely costly computations of translational–rotational–vibrational states and energies of light-molecule endofullenes. Quantum calculations on energy levels are reported for a water molecule inside C60 fullerene by means of such a systematic approach that includes all nine degrees of freedom of H2O@C60 and does not consider restrictions above them. The potential energy operator is represented as a sum of natural potentials employing the n-mode expansion, along with the exact kinetic energy operator, by introducing a set of Radau internal coordinates for the H2O molecule. On the basis of the present rigorous computations, various aspects of the quantized intermolecular dynamics upon confinement of H2O@C60 are discussed, such as the rotational energy level splitting and the significant frequency shifts of the encapsulated water molecule vibrations. The impact of water encapsulation on quantum features is explored, and insights into the nature of the underlying forces are provided, highlighting the importance of a reliable first-principles description of the guest–host interactions.

DNA Dynamics under Periodic Force Effects.

The sensitivity of DNA to electromagnetic radiation in different ranges differs depending on various factors. The aim of this study was to examine the molecular dynamics of DNA under the influence of external periodic influences with different frequencies. In the present paper, within the framework of a mechanical model without simplifications, we investigated the effect of various frequencies of external periodic action in the range from 1011 s−1 to 108 s−1 on the dynamics of a DNA molecule. It was shown that under the influence of an external periodic force, a DNA molecule can perform oscillatory movements with a specific frequency characteristic of this molecule, which differs from the frequency of the external influence ω. It was found that the frequency of such specific vibrations of a DNA molecule depends on the sequence of nucleotides. Using the developed mathematical model describing the rotational motion of the nitrogenous bases around the sugar–phosphate chain, it is possible to calculate the frequency and amplitude of the oscillations of an individual DNA area. Such calculations can find application in the field of molecular nanotechnology.

A Universal Strategy for Organic Fluid Phosphorescence Materials*.

It is an accepted approach to construct room-temperature phosphorescence (RTP) materials by suppressing the non-radiative decay process. However, there is limited success in developing fluid phosphorescence materials owing to the ultrafast non-radiation relaxation of vibration and collision of molecules in fluid matrixes. Here, a universal deep-eutectic-solvent strategy is proposed for developing pure organic phosphorescent fluid materials that are able to generate effective phosphorescent emissions at both room temperature (ΦRTP,293 K ≈30 %) and even higher temperature (ΦRTP,358 K ≈4.53 %). Based on these findings, a qualitative analytical method was developed for leak detection and a quantitative analytical technique was further validated to help visually identify the heat distribution of irregular surfaces. This advancement empowers the current organic phosphorescent system offering an alternative to determine moisture and heat from non-invasive photoluminescence emission colors.

A Universal Strategy for Organic Fluid Phosphorescence Materials**

AbstractIt is an accepted approach to construct room‐temperature phosphorescence (RTP) materials by suppressing the non‐radiative decay process. However, there is limited success in developing fluid phosphorescence materials owing to the ultrafast non‐radiation relaxation of vibration and collision of molecules in fluid matrixes. Here, a universal deep‐eutectic‐solvent strategy is proposed for developing pure organic phosphorescent fluid materials that are able to generate effective phosphorescent emissions at both room temperature (ΦRTP,293 K≈30 %) and even higher temperature (ΦRTP,358 K≈4.53 %). Based on these findings, a qualitative analytical method was developed for leak detection and a quantitative analytical technique was further validated to help visually identify the heat distribution of irregular surfaces. This advancement empowers the current organic phosphorescent system offering an alternative to determine moisture and heat from non‐invasive photoluminescence emission colors.

STUDY OF THE MOLECULAR STRUCTURE OF VALINE BY QUANTUMCHEMICAL CALCULATIONS

In this paper, calculations were performed in an isolated system using ab initio and Density Functional Theory (DFT) approaches to investigate the mechanism of molecular complex formation in valine, an amino acid. Calculations have represented that the valine molecule has intramolecular hydrogen bonds and that intermolecular hydrogen bonds are used to generate dimer and trimer complexes. The Raman spectral line (?? (OH) = 3749 cm−1 ) corresponding to the O-H vibration of the valine molecule shifted to a lower frequency of 343.9 cm-1 at the O-H bond in the trimer complex and 1533.2 cm-1 at the O-H bond due to intermolecular hydrogen bonding

Low-frequency vibrations of water molecules in DNA minor groove.

Water molecules around the DNA form the hydration shell having different structural and dynamical features in different regions of the double helix. In the DNA minor groove, water molecules are highly ordered and in the case of AT nucleotide sequence, the formation of a hydration spine is observed. In the present research, the vibrations of the hydration spine have been studied to establish the mode of translational vibrations of water molecules in the DNA low-frequency spectra (water-spine vibrations). Using the developed phenomenological model with the parameters determined for different nucleotides of the DNA fragment CGCGAATTCGCG, the frequencies of vibrations of the hydration spine have been obtained within 185 ± 20 cm[Formula: see text] depending on type of nucleotide. The obtained frequencies are in the same region as the translational vibrations of water molecules in the bulk. To select the mode of water-spine vibrations from those modes that are present in the bulk water, the dynamics of DNA with different nucleotide contents has been analyzed, and the possible influence of heavy water has been estimated. The determined features of the mode of water vibrations in the hydration spine of DNA minor groove indicate that this mode may be observed in the experimental spectra.

Fourier transform infrared spectrophotometer with attenuated total reflectance (FTIR-ATR) for analysis of uroliths in caprine species

Pathophysiology of obstructive urolithiasis in goats are multifactorial involving management, nutritional and hormonal factors. Analysis of the composition of a particular urolith would aid in understanding the aetiopathogenesis of the calculi which can facilitate establishment of appropriate treatment and prevention protocols. Four cases of chronic obstructive urolithiasis in male goats presented to University Veterinary Hospital were surgically managed by tube cystotomy. The calculi extracted from the bladder were subjected to Fourier transform infrared spectrophotometer with attenuated total reflectance (FTIR-ATR) to identify the composition of the calculi. The infrared wavelength bandwidths of H-O-H stretching vibrations, H-O-H bending modes of vibrations of water molecules, N-H symmetric stretching vibrations, N-H bending vibration and N-H asymmetric bending vibration in NH4+ unit’s ionic phosphate were compared with the available reference spectrum of wavelength and were found to be identical and comparable with the standard infrared wavelength of struvite calculi.

Research on operation parameters and properties of flue gas on adsorption of As2O3 by γ-Al2O3: An experiment and simulation study

How operation parameters (e.g. flow speed of flue gas and temperature) and flue gas properties (e.g. contents of SO2, NOx etc.) affect As2O3 adsorption by γ-Al2O3 under the condition of selective catalytic reduction (SCR) is the key to protecting catalyst from poisoning and preventing it being emitted into environments. The patterns of mentioned influence factors affecting adsorption of As2O3 have been investigated via experimental studies combined with molecular dynamics (MD) simulation calculations. According to the results of experiments and MD simulation, within the selected specific range of flue gas flow speed, As2O3 could be adsorbed effectively. In the meantime, with higher temperature, the thermal vibration of As2O3 molecule gets more intense and compromises the adsorption. Also, different flue gas contents affect As2O3 adsorption in different chemical and physical means. This research could provide valuable information for power plants and subsequent studies in related area.

A Theoretical Study of Vibrational and Optical Properties of Isatin

In this study, density functional theory (DFT) calculations performed by using both non-periodic and periodic approaches have been employed to better understand the vibrational behavior of the N–H group, as well as some optical properties of isatin. The optimized molecular geometry and crystal structure obtained by using the isolated molecule, discrete water solvation, and solid-phase models are first presented. Then, starting from the optimized crystal structure obtained by using periodic boundary conditions, new calculations have been performed to predict the N–H stretching band position. These calculations show that the band previously observed experimentally at around 3445 cm−1 cannot be assigned to the N–H stretching mode. The origin of this band is attributed here to an external experimental factor due to the hygroscopicity of the sample. This explanation is supported by tracking the bands due to stretching and bending vibrations of water molecules in the calculated IR spectrum of isatin dimer-(H2O)3. Moreover, other DFT computations are carried out to predict some optical properties of the title compound like the dielectric function e(ω), conductivity function σ(ω), refractive index n(ω), and extinction coefficient k(ω). Here, e(ω), σ(ω), n(ω), and k(ω) are plotted for three different polarization directions of the incident electromagnetic wave: [100], [010], and [001]. The obtained results confirm the optical anisotropy character of isatin crystal.

Local and Normal Modes of OH Stretching Vibration in Hydrogen-Bonded Water Molecules

Local and Normal Modes of OH Stretching Vibration in Hydrogen-Bonded Water Molecules

Ion spectroscopy in methane activation.

This review is devoted to ion spectroscopy studies of complexes relevant for the understanding of methane activation with metal ions and clusters. Methane activation starts with the formation of a complex with a metal ion. The degree of the interaction between an intact methane molecule and the ion can be monitored by the perturbations of C–H stretch vibrations in the methane molecule. Binding mediated by the electrostatic interaction results in a η3 type coordination of methane. In contrast, binding governed by orbital interactions results in a η2 type coordination of methane. We further review the spectroscopic characterization of activation products of metal–methane reactions, such as the metal–carbene and carbyne products resulting from the interaction of selected 5d metals with methane. The focus of recent research in the field has shifted towards the investigation of interactions between methane and metal clusters. We show examples highlighting that metal clusters can be more reactive in methane activation reactions.

Mid-Infrared Photodetection of Type-II Dirac Semimetal 1T-PtTe2 Grown by Molecular Beam Epitaxy.

Mid-infrared (MIR) photodetection is of significance in civil and military applications because it shows superiority in absorbing the vibration of various molecules and covering atmospheric transmission windows. Recently, the PtTe2, a typical type-II Dirac semimetal, has come under the spotlight due to its unique photodetection sensibility in the MIR region and robust stability in the atmosphere. Here, the high-quality and large-scale 1T-PtTe2 thin films with air stability were grown by molecular beam epitaxy. Broadband photoresponse of the photodetectors of PtTe2 from 420 nm to 10.7 μm shows high responsivity and detectivity of 0.2 mA W-1 and 2.6 × 107 Jones at 10.7 μm and 1.6 mA W-1 and 2.2 × 108 Jones at 4.7 μm under the atmosphere, respectively. Moreover, the photodetectors exhibit high sensitivity in visible and near-infrared regions (8.2 mA W-1 at 650 nm and 15.6 mA W-1 at 960 nm). The power- and polarization-dependent photoresponse measurements reveal the linear relationship of power photoresponse and obvious anisotropic photoresponse (the ratio of anisotropy ellipse is 8.3 at 10.7 μm), respectively. These results suggest that the PtTe2 could be expected to be an advanced photodetection material for polarization angle-sensitive detection, infrared imaging, and photodetection from the visible to MIR range.

An Overview of Acoustic Impedance Measurement Techniques and Future Prospects

In order to progress in the area of aeroacoustics, experimental measurements are necessary. Not only are they required for engineering applications in acoustics and noise engineering, but also they are necessary for developing models of acoustic phenomenon around us. One measurement of particular importance is acoustic impedance. Acoustic Impedance is the measure of opposition of acoustical flow due to the acoustic pressure. It indicates how much sound pressure is generated by the vibration of molecules of a particular acoustic medium at a given frequency and can be a characteristic of the medium.The aim of the present paper is to give a synthetic overview of the literature on impedance measurements and to discuss the advantage and disadvantage of each measurement technique. In this work, we investigate the three main categories of impedance measurement techniques, namely reverberation chamber techniques, impedance tube techniques, and far-field techniques. Theoretical principles for each technique are provided along with a discussion on historical development and recent advancements for each technique.

Effect of external electric field on the terahertz transmission characteristics of electrolyte solutions* *Project supported by the National Natural Science Foundation of China (Grant No. 61575131).

We fabricated a microfluidic chip with simple structure and good sealing performance, and studied the influence of the electric field on THz absorption intensity of liquid samples treated at different times by using THz time domain spectroscopy system. The tested liquids were deionised water and CuSO4, CuCl2, NaHCO3, Na2CO3 and NaCl solutions. The transmission intensity of the THz wave increases as the standing time of the electrolyte solution in the electric field increases. The applied electric field alters the dipole moment of water molecules in the electrolyte solution, which affects the vibration and rotation of the whole water molecules, breaks the hydrogen bonds in the water, increases the number of single water molecules and leads to the enhancement of the THz transmission spectrum.

Optimizing a coarse-grained space for approximate normal-mode vibrations of molecular heterodimers.

We applied the method of coarse-graining the intermolecular vibrations to molecular heterodimers assembled by double hydrogen bonding. This method is based on principal component analysis, by which the original atomic displacement vectors are projected onto a lower-dimensional space spanned by a basis set of translations, librations, and intramolecular vibrations of the constituent molecules. Compared with homodimers, the following points are particularly noted: (1) alignment of the constituent molecules in a non-symmetric atomic arrangement of the whole system and (2) the scheme of reordering the bases to construct an optimal coarse-grained space. We tested three schemes for reordering the intramolecular vibration vectors to determine that the best one is equivalent to size reduction based on the singular value decomposition. The coarse-graining analysis affords three parameters, Φintra, Φinter, and Φapp, which are relevant to the mechanical nature of the molecular assembly. The Φintra values account for the internal stiffness of molecules, while the Φinter values are true stiffness constants of the intermolecular force and show a good correlation with the association energies of the dimers. The Φapp values are the apparent intermolecular stiffness smaller than Φinter, as a result of compensation for neglecting intramolecular vibrations. All these values are consistent with each other under the coupled oscillator model, showing that the present coarse-graining analysis is valid for heterodimers as well as homodimers.